You would have to make the process attributes non-readable. The program name and/or executable name - one way or another - is found in /proc/N/{cmdline,comm,environ,exe,maps,numa_maps,smaps}... and short of unmounting /proc, making all sorts of programs not function the way they are supposed to, the prerequisite to do this in some way would be a change to the linux kernel source.

Even then, things like auditd(8) or selinux have ways to record what you are executing. If you don't like being looked over the shoulder, don't use the particular system.

The bigger security problem with having the command line visible is something like:

sqlplus uername/password@oracleinstance

Where users and batch applications access databases and/or embed passwords. If you cannot change this behavior you have to chroot users who have command line access on that system. chroot allows you to selectively prohibit or allow ordinary users access to commands like top, ps and other commands that use /proc. That is a standard approach to this kind of problem.